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io_uring: don't touch ctx in setup after ring fd install

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syzkaller reported an issue where it looks like a malicious app can
trigger a use-after-free of reading the ctx ->sq_array and ->rings
value right after having installed the ring fd in the process file
table.

Defer ring fd installation until after we're done reading those
values.

Fixes: 75b28affdd ("io_uring: allocate the two rings together")
Reported-by: syzbot+6f03d895a6cd0d06187f@syzkaller.appspotmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Jens Axboe 2019-10-28 09:15:33 -06:00
parent 7b20238d28
commit 044c1ab399
1 changed files with 8 additions and 4 deletions
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12
fs/io_uring.c
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@ -3829,10 +3829,6 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p)
if (ret)
goto err;
ret = io_uring_get_fd(ctx);
if (ret < 0)
goto err;
memset(&p->sq_off, 0, sizeof(p->sq_off));
p->sq_off.head = offsetof(struct io_rings, sq.head);
p->sq_off.tail = offsetof(struct io_rings, sq.tail);
@ -3850,6 +3846,14 @@ static int io_uring_create(unsigned entries, struct io_uring_params *p)
p->cq_off.overflow = offsetof(struct io_rings, cq_overflow);
p->cq_off.cqes = offsetof(struct io_rings, cqes);
/*
* Install ring fd as the very last thing, so we don't risk someone
* having closed it before we finish setup
*/
ret = io_uring_get_fd(ctx);
if (ret < 0)
goto err;
p->features = IORING_FEAT_SINGLE_MMAP;
return ret;
err: